Launch control of a hybrid electric vehicle

ABSTRACT

A method for controlling a vehicle launch using a transmission having an input, a current gear, an input clutch associated with a target gear and an output, an engine and an electric machine for driving the input, includes the steps of using the engine and the first electric machine to drive the transmission input at a desired magnitude of torque, determining a desired magnitude of torque capacity of the input clutch, determining a crankshaft speed error, determining a magnitude of a change in torque capacity of the input clutch that will reduce the crankshaft speed error, and increasing the torque capacity of the input clutch to a desired torque capacity whose magnitude is determined by adding the current magnitude of torque capacity of the input clutch and said change in torque capacity of the input clutch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a powertrain for a hybrid electricvehicle having an engine and one or more electric machines and, inparticular, to controlling torque transmitted to the drive wheels whenthe vehicle is being accelerated from a stopped or nearly stoppedcondition, called vehicle launch.

2. Description of the Prior Art

A powershift transmission is a geared mechanism employing two inputclutches used to produce multiple gear ratios in forward drive andreverse drive. It transmits power continuously using synchronizedclutch-to-clutch shifts.

The transmission incorporates gearing arranged in a dual layshaftconfiguration between the transmission input and its output. One inputclutch transmits torque between the input and a first layshaftassociated with even-numbered gears; the other input clutch transmitstorque between the transmission input and a second layshaft associatedwith odd-numbered gears. The transmission produces gear ratio changes byalternately engaging a first input clutch and running in a current gear,disengaging the second input clutch, preparing a power path in thetransmission for operation in the target gear, disengaging the firstclutch, engaging the second clutch and preparing another power path inthe transmission for operation in the next gear.

During a vehicle launch condition in a conventional vehicle whosepowertrain includes a powershift transmission, the engine andtransmission are concurrently controlled in a coordinated manner toprovide acceptable vehicle launch performance. In a powershifttransmission vehicle application, providing consistent and acceptablevehicle launch performance can be a rather difficult control problem dueto the lack of a torque converter. During a vehicle launch condition inthis type of vehicle application, the torque capacity of thetransmission clutch and slip across the clutch are carefully controlledin coordination with the engine torque to provide the desired vehicleresponse. Problems which can occur during these events include enginestall, excessive clutch slip, reduced clutch durability, dead pedalfeel, and inconsistent response are a few examples.

A powershift transmission may be used in a hybrid electric vehicle(HEV), in which one or more electric machines, such as a motor or anintegrated starter-generator (ISG), are arranged in series and parallelwith the engine. Unlike a conventional vehicle with a powershifttransmission, in a hybrid electric vehicle with a powershifttransmission, there are multiple propulsion paths and multiple powersources, the engine and electric machines, which can be used during avehicle launch condition. Therefore, a more sophisticated powershiftvehicle launch control system is needed to deal with the complexitiesand added powertrain operating modes of an HEV in response to a vehiclelaunch request from the vehicle operator.

SUMMARY OF THE INVENTION

The system and method for controlling vehicle launch in a HEV takesadvantage of additional propulsion paths and torque actuators to improvevehicle launch performance and to overcome problems and deficienciespresented by a conventional vehicle with a powershift transmission.

This control strategy supports torque blending when multiple propulsionpaths are used for propulsion during vehicle launch due to enhancedpowershift transmission control. Moreover, the control coordinatesclutch torque capacity control when propulsion assistance is provided bythe additional torque actuators, which improves clutch durability sinceclutch load is reduced accordingly. Furthermore, the control supportsbattery charging by the first electric machine during vehicle launchconditions by controlling the net crankshaft torque accordingly. Thecontrol supports multiple HEV powertrain operating modes andtransitions, automatically operates the same as a conventional vehiclewith a powershift if the additional torque actuators are not used, andis applicable to any HEV powertrain architecture that employs apowershift transmission whether the input clutches are wet or dryclutches.

A powertrain to which the control of a vehicle launch may be appliedincludes a transmission having an input, a current gear, an input clutchassociated with a target gear and an output, an engine and a firstelectric machine for driving the input. A method for controlling avehicle launch using a transmission having an input, a current gear, aninput clutch associated with a target gear and an output, an engine andan electric machine for driving the input, includes the steps of usingthe engine and the first electric machine to drive the transmissioninput at a desired magnitude of torque, determining a desired magnitudeof torque capacity of the input clutch, determining a crankshaft speederror, determining a magnitude of a change in torque capacity of theinput clutch that will reduce the crankshaft speed error, and increasingthe torque capacity of the input clutch to a desired torque capacitywhose magnitude is determined by adding the current magnitude of torquecapacity of the input clutch and said change in torque capacity of theinput clutch.

The scope of applicability of the preferred embodiment will becomeapparent from the following detailed description, claims and drawings.It should be understood, that the description and specific examples,although indicating preferred embodiments of the invention, are given byway of illustration only. Various changes and modifications to thedescribed embodiments and examples will become apparent to those skilledin the art.

DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a vehicle powertrain system to whichthe control can be applied;

FIG. 2 is a schematic diagram showing additional details of the vehiclepowertrain system of FIG. 1;

FIG. 3 is a schematic diagram of the vehicle launch control system;

FIG. 4 is a diagram illustrating the vehicle launch control methodsteps; and

FIG. 5A is a graph showing the variation with time of desired wheeltorques during vehicle launch operation produced by executing thecontrol algorithm;

FIG. 5B is a graph showing the variation of the desired torque capacityof the subject input clutch with time during vehicle launch operation;

FIG. 5C is a graph showing the variation of vehicle speed with timeduring vehicle launch operation;

FIG. 5D is a graph showing the variation of engine crankshaft speed,desired engine crankshaft speed, and clutch output speed with time ofwheel torques during vehicle launch operation;

FIG. 5E is a graph showing the variation of engine torque and CISGtorque with time during vehicle launch operation;

FIG. 5F is a graph showing the variation of transmission output torqueand ERAD torque with time during vehicle launch operation; and

FIG. 6 is a schematic diagram showing details of a powershifttransmission.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIGS. 1 and 2, a vehicle powertrain 12 includes an engine14, such as a diesel or gasoline engine; a transmission 16, such as adual wet clutch powershift transmission or another multiple ratiotransmission having no torque converter; an electric machine 18, such asan ISG (integrated starter generator) driveably connected to thetransmission input 20; and an additional electric machine 22, such as anelectric motor. Electric machine 18 provides starter/generatorcapability.

Electric machine 22, sometimes referred to as an electric rear axledrive unit (ERAD), is connected to the final drive of a rear axle 24through gearing 28 and provides additional propulsion capability ineither an electric drive or hybrid (series/parallel) drive mode. In fullFWD applications, electric machine 22 could also connected to the finaldrive of a front axle at the output of the transmission, and would bereferred to as an electric front axle drive (EFAD) unit. Power output bythe electric machine 22 drives vehicle wheels 26, 27 through ERADgearing 28 and a final drive unit 30, which is in the form of aninter-wheel differential mechanism. Similarly, the transmission output32 is driveably (mechanically) connected to vehicle wheels 34, 35through a final drive unit 36, which includes an inter-wheeldifferential mechanism.

Powertrain 12 can operate in major modes including: (1) series hybriddrive, in which engine 14 is running and producing combustion, CISG 18is generating electric power, and ERAD 22 is alternately motoring andgenerating electric power; (2) engine drive, in which CISG 18 and ERAD22 are both nonoperative and engine 14 is running, as in a conventionalpowertrain; (3) parallel hybrid drive, in which engine 14 is running,CISG 18 and/or ERAD 22 are operative to provide additional vehiclepropulsion; (4) engine starting, in which CISG 18 is motoring to startthe engine by driving the engine flywheel; and (5) engine stop, in whichengine 14 is shut down. While operating in parallel hybrid drive mode,the powertrain can operate in several sub-modes including: (3.1)parallel hybrid drive 1, in which CISG 18 is shutdown, ERAD 22 ismotoring and generating; (3.2) parallel hybrid drive 2, in which CISG 18is motoring and ERAD 22 is shutdown; (3.3) parallel hybrid drive 3, inwhich (CISG 18 and ERAD 22 are motoring; and (3.4) parallel hybrid drive4, in which CISG 18 is generating and ERAD 22 is alternatively shutdown,motoring and generating.

FIG. 2 illustrates the input clutches 40, 41, which selectively connectthe input shaft 20 of transmission 16 alternately to the even-numberedgears 42 and odd-numbered gears 43; an electronic transmission controlmodule (TCM) 44, which controls the input clutches and gearbox statethrough command signals to servos that actuate the input clutches andgearbox shift forks/synchronizers; an electronic engine control module(ECM) 46, which controls operation of engine 14; an ISC 48, whichcontrols the CISG and ERAD operations. A vehicle control system (VCS),which is not shown, issues control commands to the TCM and ECM. Each ofthe VCS, TCM and ECM includes a microprocessor accessible to electronicmemory and containing control algorithms expressed in computer code,which are executed repeatedly at frequent intervals.

There are two propulsion paths, a mechanical path and an electricalpath, which are used to meet the propulsion demand produced by thevehicle operator. The engine 14 and CISG 18 can provide vehiclepropulsion by transmitting torque through transmission 16 in themechanical propulsion path to wheels 34, 35, and the ERAD machine 28 canprovide vehicle propulsion directly in the electrical propulsion path towheels 26, 27.

The vehicle launch control uses a torque-based control scheme to controlthe torque capacity of the transmission input clutches 40, 41 and enginecrankshaft torque in response to an effective front axle propulsiondemand produced by the vehicle operator during a launch condition.

The steps of an algorithm for controlling vehicle launch using thepowertrain illustrated of FIGS. 1 and 2 are shown in the control systemdiagram of FIG. 3 and the method steps diagram of FIG. 4. The vehicleoperator's demand for wheel torque is represented by the degree to whichthe engine accelerator pedal 50 is depressed, which depression isusually referred to as accelerator pedal position, pps. An electronicsignal representing the accelerator pedal position produced by a ppssensor and an electronic signal representing the current vehicle speed52 produced by a shaft speed sensor, are received as input by a driverdemand determination function 54, which accesses in electronic memory afunction indexed by the two input variables to produce the magnitude ofthe current desired wheel torque demand T_(W) _(—) _(DES).

At 56, the desired front axle torque T_(W) _(—) _(FA) to be provided tofront wheels 34,35 by the engine 14 and CISG 18 of the mechanicalpropulsion path and the desired rear axle torque T_(W) _(—) _(RA) to beprovided to rear wheels 26, 27 by the ERAD 28 of the electricalpropulsion path are determined upon reference to the desired magnitudeof front axle torque and rear axle torque, such that the sum of thedistributed propulsion torques equals the total driver demanded wheeltorque T_(W) _(—) _(DES). The strategy for propulsion distribution maytake into account vehicle stability and dynamics constraints, energymanagement and efficiency criteria, torque capabilities of the variouspower sources, etc.

At 58, the desired ERAD torque is determined, on reference to thedistributed propulsion and the rear axle propulsion torque request T_(W)_(—) _(RA), and a command representing desired ERAD torque T_(ERAD) _(—)_(DES) is sent on communication bus 60 to the ISC 48 control interface,which command causes the ERAD 28 to produce the desired ERAD torque.

Similarly, at 59, the desired transmission output torque T_(O) _(—)_(FA) is determined and a command representing desired transmissionoutput torque, determined with reference to the distributed propulsionand the front axle propulsion torque request T_(W) _(—) _(FA), is sentto 62, where input clutch torque capacity is determined, and to 64,where engine crankshaft torque is determined. Details of the techniquesemployed at 62 and 64 are described below.

Control then passes to a powershift mode handling controller 66, whichreceives input signals representing the position of the transmissiongear selector PRNDL, actual crankshaft speed ω_(CRK) of engine 14 ,current clutch output speed ω_(CL) at the gearbox input 21, vehiclespeed VS, and the HEV powertrain operating mode. Controller 66 activatesa vehicle launch mode controller 68, provided the desired output torqueT_(O) _(—) _(FA) is equal to or greater than a predetermined magnitudeand vehicle speed is low, thereby indicating that the vehicle isoperating in vehicle launch mode and that the propulsion path thatincludes transmission 16 will be used during vehicle launch.

After controller 66 issues command 67, which activates the launch modecontrol 68, control passes to 62 where an open-loop control determinesthe magnitude of a desired open-loop input clutch torque capacity T_(CL)_(—) _(OL) _(—) _(LCH) on reference to the current transmission gear,its gear ratio, and the desired transmission output torque T_(O) _(—)_(FA).

The vehicle launch controller 68 determines at 70 the desired slipacross the input clutch 40, 41 CL_(SLIP DES) from a function stored inmemory and indexed by the current vehicle speed VS and accelerator pedalposition. The subject input clutch is associated with the target gear,i.e., the current transmission gear during launch.

At 72, the desired engine crankshaft speed ω_(CRK) _(—) _(DES) at thetransmission input 20 is determined at summing junction 74 withreference to the desired clutch slip CL_(SLIP) _(—) _(DES) and currentclutch output speed, i.e., ω_(CL) at the gearbox input 21. The desiredengine crankshaft speed ω_(CRK DES) is supplied as input to summingjunction 78. A signal representing the current clutch output speedω_(CL) is carried on communication bus 60 from the TCM 44 to summingjunction 74.

At summing junction 78, the magnitude of engine crankshaft speed errorω_(CRK) _(—) _(ERR), the difference between the desired enginecrankshaft speed ω_(CRK) _(—) _(DES) at the transmission input 20 andthe current crankshaft speed ω_(CRK), is determined and supplied asinput to a PID controller 80 or a similar closed loop controller. Asignal representing the current crankshaft speed ω_(CRK) is carried oncommunication bus 60 from the ECM 46 to summing junction 78.

In order to control slip across the subject input clutch 40, 41 duringvehicle launch, controller 80 determines a desired delta torque capacityof the subject input clutch ΔT_(CL CAP) that minimizes the currentengine crankshaft speed error ω_(CRK ERR).

At summing junction 69 the desired torque capacity of the subject inputclutch during launch T_(CL) _(—) _(CAP) _(—) _(LCH), the sum of thedesired delta torque capacity ΔT_(CL CAP) determined at 80 thatminimizes the current engine crankshaft speed error ω_(CRK ERR) and theopen loop torque capacity determined at 62 of the subject input clutchT_(CL) _(—) _(OL) _(—) _(LCH), is determined and carried on bus 60 asthe final input clutch torque capacity command 92 T_(CL) _(—) _(CAP)_(—) _(DES) and sent to TCM 44, which produces a command signal thatactuated the servo of the subject input clutch to produce the desiredtorque capacity.

Control then advances to 64, where the base torque T_(CRK) _(—) _(OL)carried by the engine crankshaft and transmission input 20 is determinedopen-loop upon reference to the desired transmission output torque T_(O)_(—) _(FA), current transmission gear, the current gear ratio, andexpected inertial torque losses associated with the rate of change ofengine crankshaft speed and combined inertias of the engine and CISG(i.e., torque lost due to engine and CISG acceleration during vehiclelaunch).

At 76, a command T_(ENG) _(—) _(DES) representing desired engine torqueand a command T_(CISG) _(—) _(DES) representing desired CISG torqueissue and are carried on communication bus 60 to an ECM 46 and to ISC 48control interfaces. These commands adjust the engine torque and CISGtorque to achieve the base crankshaft torque, such that the sum of thecommanded engine torque and commanded CISG torque equals the basecrankshaft torque T_(CRK) _(—) _(OL) from 64. The desired CISG torquecan be commanded to charge the battery is the state of charge is low,and the desired engine torque can be increased accordingly such that thesum of both commands equal the base crankshaft torque.

Control then returns to 66 to determine whether the powershift vehiclelaunch mode control 68 should be deactivated based on the currentconditions. If the current clutch slip CL_(SLIP) is minimal, crankshaftspeed ω_(CRK) is above the clutch output speed ω_(CL), and vehicle speedVS is above a threshold vehicle speed, then the vehicle launch modecontrol 68 is exited upon controller 66 issuing command signals 67 and86.

Upon exiting vehicle launch mode control, controller 66 activates an endof launch mode at 88, where a command signal T_(CL CAP RAMP) causes agradual, smooth increase in torque capacity of the subject input clutch40, 41 until the input clutch is engaged. While controller 66 activates88 for smoothly engaging the input clutch at the end of launch, thecommand signal T_(CL) _(—) _(CAP) _(—) _(RAMP) is sent to TCM 44 as thefinal input clutch torque capacity command 92.

After the subject input clutch 40,41 is smoothly engaged with zeroclutch slip at 88, controller 66 activates a locked mode at 90 and acommand T_(CL) _(—) _(CAP) _(—) _(LOCKED) is produced and carried on thecommunication bus 60 to the TCM 44 as the final input clutch torquecapacity command 92 T_(CL) _(—) _(CAP) _(—) _(DES). After the subjectinput clutch 40, 41 is fully engaged, the command T_(CL) _(—) _(CAP)_(—) _(LOCKED) issued by 90 causes the subject input clutch to becomefully engaged or locked at a clutch torque capacity well above thecurrent crankshaft torque magnitude, thereby ensuring that thetransmission will not slip.

If any of the conditions required to exit the control vehicle launchcontrol is absent, control returns to 59, where the subsequent steps ofthe control strategy are repeated.

FIG. 4 lists the steps of the vehicle launch control using the samereference numbers as are used in the sequence of steps described withreference to FIG. 3.

The graphs of FIG. 5A-5F show the variation with time of variables andparameters of the powertrain that are used or produced by executing thecontrol algorithm. For example, FIG. 5A relates to wheel torques. At100, the vehicle operator tips into the accelerator pedal during theneutral mode when neither input clutch 40, 41 is engaged, therebyincreasing the desired wheel torque T_(W DES) 104. The desired frontaxle torque 106 T_(W FA) increases as vehicle propulsion is distributed,thereby initiating a vehicle launch condition beginning at 102. Desiredwheel torque 104 T_(W DES) and desired front axle torque 106 T_(W) _(—)_(FA) differ in magnitude by the magnitude of the desired rear axletorque 108 T_(W) _(—) _(RA). At 110, rear axle torque is blended outleaving only front axle torque to drive the vehicle during the vehiclelaunch mode.

In FIG. 5B, at 102, the open-loop clutch torque capacity 112 T_(CL) _(—)_(OL) _(—) _(LCH) is commanded during the vehicle launch mode based ondesired transmission output torque T_(O) _(—) _(FA) FIG. 5B shows thevariation of the final desired torque capacity 113 of the subject inputclutch T_(CL CAP DES) and the closed loop delta input clutch torquecapacity ΔT_(CL CAP) located between graphs 112 and 113. At the end ofthe launch mode, the clutch torque capacity is ramped at 114 to smoothlyengage the transmission. Once the clutch is engaged at the end of thelaunch mode, the torque capacity of the subject input clutch is steppedup and held at 116 to fully lock the clutch and ensure the input clutchdoes not slip.

Vehicle speed 118, represented in FIG. 5C, is zero in the neutral mode,and increases throughout the launch mode.

The variation of actual engine crankshaft speed 120, desired enginecrankshaft speed 122, and clutch output speed 124 are represented inFIG. 5D. The desired slip across the subject input clutch is representedby the difference 126 between desired crankshaft speed 122 and clutchoutput speed 124. The control causes actual clutch slip to approach thedesired clutch slip as actual crankshaft speed 120 is controlled to thedesired crankshaft speed 122. The locations where actual crankshaftspeed passes through desired crankshaft speed are shown by dashedvertical lines as shown in FIG. 5D.

Engine and CISG torques, are controlled such that the sum equals thedesired open-loop crankshaft torque T_(CRK) _(—) _(OL) 128. Thedifference between the engine torque 80 and the open-loop crankshafttorque T_(CRK) _(—) _(OL) 128 represents the torque needed to charge thebattery which is the CISG torque 130 since the CISG is producinggenerating torque to charge the battery. Essentially, the engine torqueis increased to accommodate battery charging while still achieving thedesired open-loop crankshaft torque. At the point where the battery isno longer charged, the CISG torque is zero and the engine torque equalsthe desired open-loop crankshaft torque T_(CRK) _(—) _(OL) 128,

FIG. 5F illustrates the variation of transmission output torque 132T_(TRANS) _(—) _(OUT) and ERAD torque 134 T_(ERAD). The increase 136 intransmission output torque is due to increased clutch torque capacity113, shown in FIG. 5B.

The effective propulsion request for the transmission propulsion path isthe desired transmission output torque during a vehicle launch conditionafter propulsion distribution between both the mechanical and electricalpaths has been determined. This approach compensates for any vehiclepropulsion assistance provided by the ERAD during a vehicle launchcondition since the overall vehicle propulsion request can be met byboth the mechanical propulsion path and electrical propulsion path. Inaddition to supporting distributed propulsion, i.e. blending torqueproduced by the power sources, the clutch torque capacity is used toregulate clutch slip in coordination with CISG and engine torque controlduring the launch event.

FIG. 6 illustrates details of a powershift transmission 16 including afirst input clutch 40, which selective connects the input 20 oftransmission 16 alternately to the even-numbered gears 42 associatedwith a first layshaft 244, and a second input clutch 41, which selectiveconnects the input 20 alternately to the odd-numbered gears 43associated with a second layshaft 249.

Layshaft 244 supports pinions 260, 262, 264, which are each journalledon shaft 244, and couplers 266, 268, which are secured to shaft 244.Pinions 260, 262, 264 are associated respectively with the second,fourth and sixth gears. Coupler 266 includes a sleeve 270, which can bemoved leftward to engage pinion 260 and driveably connect pinion 260 toshaft 244. Coupler 268 includes a sleeve 272, which can be movedleftward to engage pinion 262 and driveably connect pinion 262 to shaft244 and can be moved rightward to engage pinion 264 and driveablyconnect pinion 264 to shaft 244.

Layshaft 249 supports pinions 274, 276, 278, which are each journalledon shaft 249, and couplers 280, 282, which are secured to shaft 249.Pinions 274, 276, 278 are associated respectively with the first, thirdand fifth gears. Coupler 280 includes a sleeve 284, which can be movedleftward to engage pinion 274 and driveably connect pinion 274 to shaft249. Coupler 282 includes a sleeve 286, which can be moved leftward toengage pinion 276 and driveably connect pinion 276 to shaft 249 and canbe moved rightward to engage pinion 278 and driveably connect pinion 278to shaft 249.

Transmission output 32 supports gears 288, 290, 292, which are eachsecured to shaft 32. Gear 288 meshes with pinions 260 and 274. Gear 290meshes with pinions 262 and 276. Gear 292 meshes with pinions 264 and278.

Couplers 266, 268, 280 and 282 may be synchronizers, or dog clutches ora combination of these.

Although the invention has been described with reference to a powershifttransmission, the invention is applicable to any conventional manualtransmission, automatic shift manual transmission, or automatictransmission that has no torque converter located in a power pathbetween the engine and transmission input.

In accordance with the provisions of the patent statutes, the preferredembodiment has been described. However, it should be noted that thealternate embodiments can be practiced otherwise than as specificallyillustrated and described.

1. A method for controlling a vehicle launch condition of a vehiclehaving a powertrain that includes a transmission having an input, acurrent gear, an input clutch associated with a target gear and anoutput, an engine and a first electric machine for driving the input,comprising the steps of: (a) using the engine and the first electricmachine to drive the transmission input at a desired magnitude oftorque; (b) determining a desired magnitude of torque capacity of theinput clutch; (c) determining a crankshaft speed error; (d) determininga magnitude of a change in torque capacity of the input clutch that willreduce the crankshaft speed error; and (e) changing the torque capacityof the input clutch to a desired torque capacity whose magnitude isdetermined by adding the current magnitude of torque capacity of theinput clutch and said change in torque capacity of the input clutch. 2.The method of claim 1 further comprising the step of using a speed ofthe vehicle and a position of an accelerator pedal to determine avehicle propulsion demand.
 3. The method of claim 1, wherein step (e)further comprises the step of increasing the torque capacity of theinput clutch along a ramp to a torque capacity that is equal to themagnitude of torque at the transmission input.
 4. (canceled) 5.(canceled)
 6. The method of claim 1, wherein step (b) further comprisesthe steps of: using a speed of the vehicle and a position of anaccelerator pedal to determine a desired magnitude of wheel torque; andusing the desired magnitude of wheel torque and a gear ratio of thecurrent gear to determine said desired torque capacity of the inputclutch.
 7. The method of claim 1, wherein step (a) further comprises thesteps of: using a speed of the vehicle and a position of an acceleratorpedal to determine a desired magnitude of wheel torque; using thedesired magnitude of wheel torque, a gear ratio of the current gear, arotating inertia of the engine, a rotating inertia of the first electricmachine, and a rate of change of engine speed to determine said desiredmagnitude of torque at the transmission input.
 8. The method of claim 1,wherein step (c) further comprises the steps of: determining a desiredslip across the input clutch; using the desired slip across the inputclutch and speed of the an output of the input clutch to determinedesired crankshaft speed; and using a difference between the desiredcrankshaft speed and a speed of the crankshaft to determine thecrankshaft speed error.
 9. (canceled)
 10. The method of claim 1 whereinstep (d) further comprises the steps of using a PID controller and thecrankshaft speed error to determine the desired change in torquecapacity of the input clutch that will reduce the crankshaft speederror.
 11. The method of claim 1 further comprising the steps of:determining whether input clutch slip is substantially zero; determiningwhether the crankshaft speed is greater than the speed of the output ofthe input clutch; determining whether the vehicle speed is greater thana predetermined vehicle speed; and discontinuing performing the vehiclelaunch control method, if all of said conditions are present.
 12. Amethod for controlling a powertrain that includes a transmission havingan input, a current gear, an input clutch associated with a target gearand an output, an engine and a first electric machine for driving theinput and a first set of vehicle wheels, and a second electric machinefor driving a second set of vehicle wheels, comprising the steps of: (A)using an operator demand for a desired wheel torque to determine adesired wheel torque at the first wheel set and a desired wheel torqueat the second wheel set; (B) operating the engine, the first electricmachine and the transmission to produce the desired magnitude of torqueat the second wheel set, and operating the second electric machine toproduce the desired magnitude of torque at the second wheel set; (C)determining a desired magnitude of torque capacity of the input clutch;(D) determining an crankshaft speed error; (E) determining a magnitudeof a change in torque capacity of the input clutch that will reduce thecrankshaft speed error; and (F) changing the torque capacity of theinput clutch to a desired torque capacity whose magnitude is determinedby adding the current magnitude of torque capacity of the input clutchand said change in torque capacity of the input clutch.
 13. The methodof claim 12, wherein step (F) further comprises the step of increasingthe torque capacity of the input clutch along a ramp to a torquecapacity that is equal to the magnitude of torque at the transmissioninput.
 14. (canceled)
 15. The method of claim 12, wherein step (C)further comprises the steps of: using a speed of the vehicle and aposition of an accelerator pedal to determine a desired magnitude oftorque at the transmission output; and using the desired magnitude oftorque at the transmission output and a gear ratio of the current gearto determine said desired torque capacity of the input clutch.
 16. Themethod of claim 12, wherein step (D) further comprises the steps of:determining a desired slip across the input clutch; using the desiredslip across the input clutch and speed of the an output of the inputclutch to determine desired crankshaft speed; and using a differencebetween the desired crankshaft speed and a speed of the crankshaft todetermine the crankshaft speed error.
 17. The method of claim 16 furthercomprising the step of using a current vehicle speed and an acceleratorpedal position to determine the desired slip across the input clutch.18. The method of claim 12 wherein step (E) further comprises the stepsof using a PID controller and the crankshaft speed error to determinethe desired change in torque capacity of the input clutch that willreduce the crankshaft speed error.
 19. The method of claim 12 furthercomprising the steps of: determining whether input clutch slip issubstantially zero; determining whether the crankshaft speed is greaterthan the speed of the output of the input clutch; determining whetherthe vehicle speed is greater than a predetermined vehicle speed; anddiscontinuing performing the vehicle launch control method, if all ofsaid conditions are present
 20. A system for controlling a vehiclelaunch condition comprising: an engine; a first electric machine; atransmission including an input and an output, the transmission beingable to operate in a current gear and a target gear; an input clutch foralternately closing and opening a drive connection between the engineand transmission input and between the first machine and thetransmission input; and a controller configured to drive thetransmission input at a desired magnitude of torque, determine a desiredmagnitude of torque capacity of the input clutch, determine a crankshaftspeed error, determine a magnitude of a change in torque capacity of theinput clutch that will reduce the crankshaft speed error, and increaseor decrease the torque capacity of the input clutch to a desired torquecapacity whose magnitude is determined by adding the current magnitudeof torque capacity of the input clutch and said change in torquecapacity of the input clutch.
 21. The system of claim 18, wherein thecontroller is further configured to increase the torque capacity of theinput clutch along a ramp to a torque capacity that is equal to themagnitude of torque at the transmission input.
 22. (canceled)
 23. Thesystem of claim 20, wherein the controller is further configured to: usea speed of the vehicle and a position of an accelerator pedal todetermine a desired magnitude of torque at the transmission output; anduse the desired magnitude of torque at the transmission output and agear ratio of the current gear to determine said desired torque capacityof the input clutch.
 24. (canceled)
 25. The system of claim 20, whereinthe controller is further configured to: determine a desired slip acrossthe input clutch; use the desired slip across the input clutch and speedof the an output of the input clutch to determine a desired crankshaftspeed; and use a difference between the desired crankshaft speed and aspeed of the crankshaft to determine the crankshaft speed error. 26.(canceled)
 27. (canceled)
 28. A system for controlling a vehicle launchcondition comprising: an engine; a first electric machine; a secondelectric machine; a transmission including an input and an output, thetransmission being able to operate in a current gear and a target gear;an input clutch for alternately closing and opening a drive connectionbetween the engine and transmission input and between the first machineand the transmission input; and a controller configured to determinefrom an operator demand for a desired wheel torque a desired wheeltorque at the first wheel set and a desired wheel torque at the secondwheel set; operate the engine, the first electric machine and thetransmission to produce the desired magnitude of torque at the secondwheel set, operate the second electric machine to produce the desiredmagnitude of torque at the second wheel set; drive the transmissioninput at a desired magnitude of torque, determine a desired magnitude oftorque capacity of the input clutch; determine a crankshaft speed error;determine a magnitude of a change in torque capacity of the input clutchthat will reduce the crankshaft speed error; and change the torquecapacity of the input clutch to a desired torque capacity whosemagnitude is determined by adding the current magnitude of torquecapacity of the input clutch and said change in torque capacity of theinput clutch.
 29. The system of claim 31, wherein the controller isfurther configured to increase the torque capacity of the input clutchalong a ramp to a torque capacity that is equal to the magnitude oftorque at the transmission input.
 30. The system of claim 31 wherein thecontroller is further configured to increase the torque capacity of theinput clutch to a torque capacity that is greater than the magnitude oftorque at the transmission input.
 31. The system of claim 31, whereinthe controller is further configured to: use a speed of the vehicle anda position of an accelerator pedal to determine a desired magnitude oftorque at the transmission output; and use the desired magnitude oftorque at the transmission output and a gear ratio of the current gearto determine said desired torque capacity of the input clutch.
 32. Thesystem of claim 31, wherein the controller is further configured to: usea speed of the vehicle and a position of an accelerator pedal todetermine a desired magnitude of torque at the transmission output; anduse the desired magnitude of torque at the transmission output, a gearratio of the current gear, a rotating inertia of the engine, a rotatinginertia of the first electric machine, and a rate of change ofcrankshaft speed to determine said desired magnitude of torque at thetransmission input.
 33. The system of claim 31, wherein the controlleris further configured to: determine a desired slip across the inputclutch; use the desired slip across the input clutch and speed of the anoutput of the input clutch to determine desired crankshaft speed; anduse a difference between the desired crankshaft speed and a speed of thecrankshaft to determine the crankshaft speed error.
 34. (canceled) 35.(canceled)